Turbochargers are a type of forced induction system for internal combustion engines which use the exhaust flow, entering the turbine housing from the engine exhaust manifold, to drive a turbine wheel, which is located in the turbine housing. To control the energy to the turbine wheel, and thus the boost output of the turbocharger, which, in turn, affects the power output of the engine, a variable geometry configuration of the turbine stage is used to control said turbine energy. In the case of a VTG, an actuator is used to control the turbine power.
While the highest exhaust temperature of a gasoline engine is up to 1050° C., the exhaust temperature of a large Diesel engine is typically up to 760° C. With increasing demands for improved emissions, engine combustion chamber temperatures not only run hotter, but aerodynamic demands, such as lower hood lines and lower engine compartment airflow, combine to produce an increasingly thermally hostile environment for engine components, internal and external.
With the requirement for ever tighter emissions, electronic controls have replaced more thermally accepting control-force mediums such as vacuum, hydraulic and air pressure. Electronics used in automotive applications are not particularly tolerant of temperatures above 100° C. Printed Circuit Boards (PCBs) have to be specially manufactured to even meet the 100° C. threshold. Of the components within a VTG actuator enclosure, gears, shafts, electric motors and sensors, the PCBs are the most intolerant of excess temperature.
On VTG or wastegate electronically controlled turbochargers, the actuator has to be located in close proximity to the turbocharger because the actuator mechanically controls valves or vanes in the turbine stage of the turbocharger. This close proximity is driven by the requirement of the article being driven (vanes or valves) and is exacerbated by the requirement for a tight envelope surrounding the engine.
Electronic components are often air or water-cooled to protect the thermally sensitive components. Sometimes they are mounted remotely such as on the cabin firewall or even under the front seats of the vehicle in the quest for a more thermally and vibration friendly environment. Turbocharger electronic actuators however must be mounted either on, or close to, the turbine housing. Sometimes the turbocharger itself incorporates a water-cooled bearing housing which lessens the electronic actuator ambient thermal issues. The electronic VTG actuator, which is associated with the subject of this invention, is typically mounted directly to the turbine housing so that the controls can be assembled, datumed, and validated at the factory where the turbocharger is assembled, to neutralize manufacturing variances.
A typical electronic actuator (10) is shown in FIGS. 1 and 2 mounted directly to a typical turbocharger housing (1) via a cast iron casting bracket (2) which is part of the turbine housing assembly. A signal from an engine controller unit (ECU) commands rotation of an actuator shaft (11) which rotates an actuator drive arm (12). Connected by a pin, bolt, or stud (14) to the actuator drive arm (12) is a linkage. The linkage, depicted in FIG. 6, typically has a shaft (16) mechanically attached to a pair of rod-ends which are free to rotate a few degrees about the control linkage centerline, but are constrained longitudinally. This arrangement ensures centerline forces on the shaft, which minimizes bending loads on the linkage. The pin, bolt or stud (14) is mechanically attached to a bore (9) in the ball (8). The ball (8) is constrained but free to rotate in the head (3) of the rod-end.
In FIG. 6, the driving rod-end (15f) (hereinafter “f” refers to female connector and “m” refers to male connector) is attached to the actuator end of the shaft (16), and the driven rod-end (7f) is attached to the VTG end of the shaft (16). The driven rod-end (7f) is connected by a pin, bolt or stud (6) to the driven arm (4) of the VTG. The driven arm is connected such that any rotation of the driven arm (4) is transferred to a shaft in the VTG upon which the driven arm is attached. All movement commanded by the engine ECU to the VTG actuator (10) results in movement of the driving arm, connecting linkage and driven arm to the shaft in the VTG, which moves the VTG vanes to control the exhaust flow to a turbine wheel.
The inventor discovered, while performing unrelated testing, that a Diesel engine, at the test condition, had an exhaust temperature of 650° C., which produced a turbine housing outer skin temperature in excess of 435° C. The VTG vanes are wetted by the exhaust flow so they see the exhaust temperature (which, for the engine being tested had a design a maximum of 760° C.) directly impinging on the surfaces of the vanes. Some heat energy is lost in conduction through the internal linkages to the VTG shaft. The VTG shaft is however mechanically connected to the VTG driven arm (4) with a large contact surface area such that thermal transference via conductance is, unfortunately, efficient. The tests showed that the driven rod end (7f) (VTG end rod-end) on the linkage had a temperature of 150° C. The rod-ends (15 and 7) and the shafts (16) are typically steel with a bronze or plastic bearing surface in the ball joint so that much of the heat from the VTG shaft is transferred by conductance via the drive pin (14) and actuator drive arm (12) to the actuator shaft (11). The tests indicated that a temperature of 150° C. at the VTG driven arm (4) resulted in a temperature of 121.5° C. at the actuator drive arm (12), with the standard linkage.
A failure in the electronics in the actuator is a failure of the turbocharger. To protect the sensitive electronics in the actuator (10), many methods are employed:                Some VTG installations have water cooled actuators, which is a relatively complex, potentially unreliable, and expensive solution.        Some VTG installations have water cooled bearing housings, which is a relatively common, albeit expensive solution, but which does improve the thermal conditions inside and around the turbo.        Some VTG installations have actuators cooled by forced air circulation and shielding, which is difficult to execute, and the shielding is difficult to maintain.        Some VTG installations have the actuator removed relatively far from the VTG and connected to the VTG via a long connecting rod. This causes problems in actuator shaft stiffness and damping VTG casting issues due to the length of the bracket design of the casting envelope, and, above all, moving the actuator away from the VTG is architecturally challenging.        
A typical control linkage configuration is determined by the diameter of the drive pin (14), or bore in the ball joint, which typically is paired with a male (24), or female (25) thread in the barrel or neck of the rod-end. For example, the control linkage, depicted in FIG. 6 has a 6 mm drive pin (14) and a shaft (16) 6 mm in diameter. This can cause durability problems because, while the rod end itself is capable of transmitting static centerline loads, the control linkage shaft can bend, or vibrate in resonance with an excitation from the engine. Either of these problems can cause premature wear-out of the ball joints in the rod end.
So it is clear that there is a need for a cost-effective solution for retarding heat energy transfer from the turbine housing through the control linkage to the actuator in such a manner that it does not compromise the design and durability of the engine or components. It would be desirable to cure at the same time the problem of control linkage shaft bending or vibration.